The capacity and kinetics of CO2 sorption for Na2CO3 and K2CO3 under moist conditions were studied to determine the mechanism for CO2 capture under ambient conditions. Bicarbonate formations of Na2CO3 and K2CO3 were examined by thermogravimetric analysis under various CO2 concentrations and humidity, and the accompanying structural changes of Na2CO3 and K2CO3 were exhibited by X-ray diffraction (XRD). Also, morphological changes were observed during the reaction by scanning electron microscopy (SEM). The structural and morphological changes during the reactions were then related to the kinetic and exothermic properties of the CO2 sorption of Na2CO3 and K2CO3 together with H2O from XRD and SEM measurements. The modification of Na2CO3 and K2CO3 for improvement in regeneration temperature and CO2 occlusion kinetics were also examined by substitution of different metal ions or formation of nanostructured materials.